Hydrodesulfurization process

ABSTRACT

Low sulfur diesel oil and low sulfur fuel oil are produced by a process which permits the minimum production of materials boiling in the gasoline range. A catalytic hydrodesulfurization process reduces the sulfur content of the portion of the feed charge which is subsequently fractionated into the desired diesel fuel and fuel oil. Hydrocarbons produced in the desulfurization process boiling within the motor fuel boiling range are catalytically cracked to yield substantial quantities of C1 to C4 hydrocarbons.

United States Patent [151 3,668,1 1 2 Parker et al. 1 June 6, 1972 54] HYDRODESULFURIZATION PROCESS 3,481,864 12/1969 Hallman et al ..208/210 [72] Inventors: Levi C. Parker, Port Arthur; Odes B.

Robertson, Groves, both of Tex. 'f Exam" ler De]ben Assistant Examiner-G. J Crasanalus AS51811: Texico New York, NY. Attorney-K. E. Kavanagh and Thomas H. Whaley 22 Filed: Dec. 6, 1968 [57] ABSTRACT [2]] Appl. No.: 781,788

Low sulfur diesel oil and low sulfur fuel oil are produced by a process which permits the minimum production of materials ISZI [1.5. .l v. .....2l)8/89 boiling in the gasoline range A cataiytic hydrodesulfurizafion I f'" "1 "(J08 23/00 process reduces the sulfur content of the portion of the feed (Search 89, charge is subsequently fractionated into the desired 208/61 210 diesel fuel and fuel oil. Hydrocarbons produced in the desulfurization process boiling within the motor fuel boiling range [56] References Cited are catalytically cracked to yield substantial quantities of C to UNITED STATES PATENTS C4 hydrcarbons- 3,260,663 7/ l 966 Inwood et al. ..208/59 4 Claims, 1 Drawing Figure 2a flcyc/ec/ /& 4kg /2) fiyfipwen'ure 24 \s'eporQ/ J4 j y\ 30 i2 073/7/2/ Zane 22 C /'A/ /8- fleas/cw 4 {9 e. fig d'adend/ar/ia/f t 46 I (lf fi gfi/r- /2 a 46 a, a, L0/a@- 44 I e 0 a?! IY/IOA/ fiacl flar/ 5:7

HYDRODESULFURIZATION rnocsss BACKGROUND OF THE INVENTION This invention relates to the production of low sulfur diesel fuel and low sulfur fuel oil. In one of its more specific aspects, the present invention relates to a process for reducing the sulfur content of diesel fuel and fuel oil while any hydrocarbons boiling in the gasoline range produced as a by-product from the desulfurization process are converted to C C hydrocarbons. In particular, this invention relates to a combination of processes wherein the sulfur content of a charge stock is reduced in a catalytic hydrodesulfurization process followed by a catalytic hydrocracking of the gasoline fraction and a separation of the liquid effluent from the desulfurization process to produce the low sulfur diesel fuel and low sulfur fuel oil. Any gasoline fractions produced in these operations are recycled to extinction to either the hydrodesulfurization zone or the hydrocracking zone.

Recent concern over the potential hazards of air pollution has lead to studies which identify sulfur compounds in the atmosphere as being particularly troublesome and suggest a major reduction in the emission of sulfur compounds into the atmosphere. One means offered for achieving this result is to reduce the sulfur content of fossil fuels used in stationary power and electric generating plants. Many methods have been suggested and others are currently the source of intensive research to achieve the desired result of reducing the sulfur content of diesel fuels and heavy fuel oils. Hydrogenation processes, including catalytically promoted techniques, have been suggested recently as a means of achieving the desired results. One process being employed is to hydrotreat a fuel oil charge stock prior to its fractionation into the desired end roducts, diesel fuel and fuel oil. In most of these hydrogenation processes a portion of the charge stock is converted to materials boiling below the diesel oil range. These lighter materials find a variety of uses in many geographic areas, as feed stocks for petrochemical manufacture and liquified petroleum gas, LPG, and as gasoline blending stocks. However, in those areas where gasoline demand is low but LPG requirements are substantial, a novel scheme for desulfurizing fuel oils with minimum or no gasoline manufacture while producing substantial quantities of LPG would find particular utility.

SUMMARY OF THE INVENTION By means of the process of our invention, both diesel fuels and fuel oils having reduced sulfur content, may be produced with minimum or no gasoline yield. Although a catalytic hydrodesulfurization process may be operated to substantially reduce the sulfur contents of both diesel oil and fuel oil, substantial quantities of materials boiling in the range below diesel oil are produced by this process the amount of these by-products being directly proportional to the severity of the desulfurization process. To minimize or eliminate that fraction boiling in the gasoline range, the process of our invention combines a hydrocracking step with the desulfuriz'ation operation to convert the gasoline fraction to C C hydrocarbons.

More particularly, in the process of our invention a sulfurcontaining hydrocarbon liquid charge stock suitable for the production of diesel oil and fuel oil is contacted, together with hydrogen, in a hydrodesulfurization zone with a hydrodesulfurization catalyst under conditions effecting a reduction in the sulfur content of said charge stocks. The conditions in the hydrodesulfurization zone are selected so as to maintain substantially all materials boiling below diesel oil in the vapor state. The vaporous effluent is removed from the hydrodesulfurization zone and contacted in a hydrocracking zone with a hydrocracking catalyst under conditions to convert a substantial portion of said vaporous effluent to a hydrocarbon mixture boiling below the motor gasoline range and consisting substantially of C C, hydrocarbons. A motor fuel fraction, also referred to hereinafter as a gasoline fraction, is recovered from the effluents from the hydrocracking zone and the hydrodesulfurization zone and passed to the hydrodesulfurization zone as feed thereto to aid the liquid phase desulfurization reaction. Optionally, this motor fuel fraction may be introduced directly into the hydrocracking zone as feed thereto. The C,C, hydrocarbons produced in the process of my invention are recovered at several points in the process scheme and are combined for use as petrochemical charge stocks or as valuable components for inclusion in liquified petroleum gas, LPG. Those materials boiling above the motor gasoline range are removed from the hydrodesulfurization zone as a liquid effluent and separated by, for example, a fractionator into a diesel oil fraction having a sulfur content substantially below that of the diesel fuel fraction of the charge stock and a fuel oil fraction having a sulfur content substantially below that of the fuel oil fraction of the charge stock.

A portion of the diesel oil cut will emerge from the hydrodesulfurization zone as a vapor and will pass into the hydrocracking zone. A portion of this vaporous diesel oil cut will be hydrocracked, while the remainder will be recovered as diesel oil in the fractionator along with the diesel oil removed as a liquid from the hydrodesulfurization zone. A very small portion of the gasoline fraction will emerge from the hydrodesulfurization zone as a liquid and will be recovered in the fractionator. This gasoline fraction will be recycled to either the hydrocracking zone or the hydrodesulfurization zone as discussed above.

To reduce the quantity of diesel oil which would otherwise be vaporized into the hydrocracking zone, the two reaction zones are operated at different temperatures with the hydrocracking zone temperature being 50 to F. lower than the hydrodesulfurization zone. This may be achieved in any of several ways. For example, cooling coils may be placed in upper portion of the liquid body of the reaction mixture in the hydrodesulfurization zone, above the catalyst bed. Another method would be to place several bubble cap stripping trays between the two zones.

BRIEF DESCRIPTION OF THE DRAWING The accompanying drawing is a schematic flow diagram of an embodiment of the process units and flow systems suitable for carrying out the process of the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT In accordance with the present invention, a sulfurcontaining hydrocarbon feed stock suitable for the production of substantial quantities of diesel oil and fuel oil is processed in a sequence of catalytic hydrodesulfurization and catalytic hydrocracking to ultimately yield diesel oil of low sulfur content, fuel oil of low sulfur content and substantial quantities of LPG with a minimum or no gasoline yield.

Our invention may be understood from the following detailed description, taken with reference to the accompanying drawing which illustrates diagramatically an embodiment for practicing the method of my invention.

A charge stock such as a reduced crude is introduced into the system through line 10 and, with hydrogen from line 12, passes through line 14 into the hydrodesulfurization zone 16 of reactor 18 where it is contacted with a bed of hydrodesulfurization catalyst. The hydrocarbon reactants and a major portion of the hydrocarbon products therefrom which boil above the gasoline range are maintained in the liquid state within zone 16. The level of the liquid is maintained within reactor 18 at a point above the hydrodesulfurization catalyst bed. Cooling coil 19 cools the upper portion of the liquid thereby reducing the quantity of hydrocarbons boiling in the diesel oil range which would otherwise pass from the hydrodesulfurization zone as a vapor. The resultant vaporous phase comprising hydrogen, hydrocarbons boiling below the diesel oil range, reaction products boiling below the diesel oil range and a portion of the hydrocarbons boiling in the diesel oil range, pass through the liquid in the lower portion of reactor 18 into hydrocracking zone 20 in the upper portion of the reactor which containsa bed of hydrocracking catalyst. Additional quantities of hydrogen may be introduced into the hydrocracking zone through line 22. Reaction products from the hydrocracking zone pass through line 24 into high pressure separator 26 from which a hydrogen-containing gas is removed through line 28 and recycled for reintroduction into reactor 18. The liquid from the separator passes through line 30 into stabilizer 32 where a gaseous fraction of C and lighter hydrocarbons is removed through line 34. The liquid from the stabilizer, which is a hydrocarbon mixture boiling within the gasoline and diesel oil ranges is removed through line 36.

Returning to reactor 18, the liquid phase reaction products from the hydrodesulfurization zone 16 are removed under liquid level control through line 37 to high pressure separator 38 from which a hydrogen-containing gas is removed through line 39 and combined with the hydrogen-containing gas in line 28. Liquid from separator 38 flows through line 40 to stabilizer 41 where a gaseous fraction of C and lighter hydrocarbons is removed through line 42. The liquid from the stabilizer passes through line 44 and is combined with the effluent passing from stabilizer 32 through line 36. The combined stream passes into fractionator 46 for separation of the liquid effluent into various products. An overhead cut of C and lighter hydrocarbons is removed through line 48. Materials boiling within the gasoline range are removed through line 50 and recycled back to the reactor either through line 52 for reintroduction with the feed to the hydrodesulfurization zone or through line 54 for introduction into the hydrocracking zone. The low sulfur products, diesel oil and fuel oil, are removed from fractionator 46 through lines 56 and 58, respectively.

Since the process of our invention produces low sulfur diesel oil and low sulfur fuel oil, any of the charge stocks normally used to produce these fuel oils may be employed in our process. Suitable charge stocks include hydrocarbon fractions preferably boiling above the gasoline range, i.e., boiling above about 400 F and preferably boiling within the range of about 400 l,050 F. However, stocks containing a gasoline fraction may be employed. Useful charge stocks include crude oils, atmospheric and vacuum reduced crudes, atmospheric and vacuum gas oils, visbroken stocks, delayed coker stocks, thermal or catalytically cracked stocks and similar petroleum fractions. Charge stocks containing substantial quantities of sulfur may be desulfurized by the process of our invention with minimum yield of gasoline. Sulfur contents of up to about wt. percent can be handled quite easily. The quantity of sulfur present in the charge stock and the minimum level of sulfur desired in the products will dictate the severity of the operation which in turn controls the percentage of sulfur removal as well as the ultimate yield of by-products, i.e., the C C, hydrocarbons.

Hydrogen used in the process of the present invention may be obtained from any suitable source. The hydrogen need not be pure but may contain as much as 50 percent impurities. In this respect, the term, hydrogen," as used in the present specification and claims includes dilute hydrogen. Preferably a gas containing at least 70 percent hydrogen is used. Suitable sources are catalytic reformer by-product gas, electrolytic hydrogen and hydrogen produced by the partial oxidation of carbonaceous material followed by shift conversion and CO removal. Since the efficiency of the process depends to some extent on the partial pressure of the hydrogen, advantageously the efficiency for a given total pressure on the system increases as the hydrogen purity is increased.

- The hydrodesulfurization catalyst may be any one of the Well known catalysts used for this purpose. These catalysts are conventionally composed of two components, a hydrogenating component and a catalyst support. The hydrogenating component comprises metals of Group VI and Group VIII such as, nickel, iron, tungsten, cobalt, palladium, platinum, molybdenum, their oxides or sulfides and mixtures thereof. The catalyst support may be any of the non-acidic or mildly acidic bases such as alumina, boria-alumina and silica-alumina. Particularly suitable hydrogenating catalysts comprise cobalt and molybdenum on alumina or silica-alumina, nickel and molybdenum on alumina or silica-alumina, and nickel sulfide and tungsten sulfide on boria-alumina.

The hydrocracking portion of the operation is carried out in the presence of any of the well known hydrocracking catalysts which are conventionally composed of a cracking component which forms the major portion of the catalyst composite and a hydrogenating component which generally is supported on the cracking component. Suitable hydrogenating components comprise the metals of Group V1 and Group VIII such as, for example, nickel, iron, tungsten, cobalt, palladium, platinum, molybdenum, their oxides or sulfides and mixtures thereof. The cracking component and the support for the hydrogenating component include such materials as natural cracking catalyst, boria-alumina, synthetic silica-alumina, silica-magnesia, silica gel, and such natural and synthetic crystalline alumino-silicates as Zeolite X and Y. Examples of useful hydrocracking catalysts include nickel sulfide and tungsten sulfide on silica-alumina and nickel sulfide and tungsten sulfide on Zeolite Y.

The operating conditions which are preferred in the operation of our invention include a pressure of SOC-3,000 psig, a temperature of 500-1,000 F., a space velocity (LI-ISV) of 0.25 to 5 v/hr/v and a hydrogen rate of LOGO-40,000 SCF/B of fresh feed. To minimize the amount of diesel oil passing to the hydrocracking zone, we prefer that the hydrocracking zone be operated about 50 to F. below the hydrodesulfurization zone.

The following example illustrates the advantage of our invention in a process exemplified by the flowplan of the drawmg.

A 1:1 blend of a reduced Arabian crude and reduced Safaniya crude having the properties set forth in Table 1 below is introduced into the hydrodesulfurization zone of a reactor. The lower portion of this reactor contains a fixed bed of a hydrodesulfurization catalyst, nickel molybdate supported on an alumina base, and sold under the trade name Aero HDS3. The upper portion of the reactor, the hydrocracking zone, contains a fixed bed of a commercial hydrocracking catalyst, nickel sulfide and tungsten sulfide supported on silica-alumina, and sold under the trade name Harshaw Ni 4401-15. The properties of the charge stock and its yield analysis are presented in Table I below.

TABLE I Properties of 1:1 Blend of Reduced Arabian and Reduced Safaniya Crudes And Products Obtained Therefrom Charge Diesel oil Fuel oil Stock (400-650650F.

The operating conditions used in the reactor maintain a major portion of the materials boiling above the gasoline range as a liquid in the hydrodesulfurization zone of the reactor. Gaseous reaction products, C to C hydrocarbons, C hydrocarbons, C 400 F. gasoline, and a portion of the diesel oil pass in the vapor state to the hydrocracking zone. Cooling coils located in the portion of the liquid above the bed of hydrodesulfurization catalyst remove sufficient heat to reduce the temperature of surface liquid thereby maintaining the operating temperatures of the two zones at about a 90 F. delta tee. This reduces the quantity of diesel oil which would otherwise pass as a vapor from the hydrodesulfurization zone to the hydrocracking zone. The operating conditions used within the two zones are shown in Table ll below.

Fresh Liquid feed. Volume ratio The severity of the desulfurization process within the lower portion of the reactor converts 30 vol. percent of the 650 F. portion of the charge stock to materials lighter than 650 F. The desulfurized liquid is removed from the hydrodesulfurization zone for recovery of diesel oil and fuel oil products. Materials lighter than diesel oil, i.e., any gasoline produced in the operation, are recycled to extinction. On a once through basis, substantial quantities of low-sulfur diesel oil and lowsulfur fuel oil are recovered together with a significant yield of C to C hydrocarbons. No materials boiling in the gasoline range are produced. Product yield, on a weight basis, is presented in Table Ill below.

It is seen that a charge stock which is suitable for the production of diesel oil and fuel oil but which contains 3.3 wt. percent sulfur can be processed by the process of our invention to yield substantial quantities of diesel fuel and fuel oil having substantially reduced sulfur contents and with no gasoline yield.

Obviously many modifications and variations of our invention as hereinbefore set forth, may be made without departing from the spirit and scope thereof and therefore only such limitations should be imposed as are indicated in the appended claims.

We claim:

I. A process for the production of diesel oil having a low sulfur content, fuel oil having a low sulfur content and C -C hydrocarbons which comprises:

a. contacting a sulfur-containing hydrocarbon liquid charge stock and h drogen in a h drodesulfurization zone with a hydrodes nzation cat yst under conditions efiectin g a reduction in the sulfur content of said charge stock, said conditions maintaining substantially all components boiling below diesel oil in the vapor state, passing said vapor from said hydrodesulfurization zone as a first vaporous effluent to a hydrocracking zone,

contacting said first vaporous effluent in said hydrocracking zone with a hydrocracking catalyst under conditions effecting conversion of said vaporous effluent to hydrocarbons boiling below the gasoline range, said conditions in step (c) comprising a reaction temperature 50l 50 F. lower than in step (a),

d. recovering a C and lighter hydrocarbon fraction from the hydrocracking zone efiluent,

e. recovering a C and lighter hydrocarbon fraction from the hydrodesulfurization zone liquid efiluent,

f. separating the remaining liquid effluents from steps (d) and (e) into fractions comprising:

i. a gasoline fraction,

ii. a diesel oil fraction having a sulfur content substantially below that of the diesel oil fraction of the charge stock, and

iii a fuel oil fraction having a sulfur content substantially below that of the fuel oil fraction of the charge stock, and

g. passing said gasoline fraction to either step (a) or step (c) as feed thereto.

2. A process according to claim 1 wherein the conditions of steps (a) and (c) comprise the following ranges:

a pressure of SOC-3,000 psig,

a temperature of 5001,000 F., and

a space velocity of O.255.0 v/hr/v.

3. A process according to claim 1, including the following additional steps:

(h) recovering from said hydrodesulfurization zone and said hydrocracking zone a gaseous stream comprising hydrogen and (i) passing said stream to said hydrodesulfurization zone.

4. A process according to claim 2 which includes a hydrogen feed in step (a) of LOCO-40,000 SCF/B of said charge stock. 

2. A process according to claim 1 wherein the conditions of steps (a) and (c) comprise the following ranges: a pressure of 500-3,000 psig, a temperature of 500*-1,000* F., and a space velocity of 0.25-5.0 v/hr/v.
 3. A process according to claim 1, including the following additional steps: (h) recovering from said hydrodesulfurization zone and said hydrocracking zone a gaseous stream comprising hydrogen and (i) passing said stream to said hydrodesulfurization zone.
 4. A process according to claim 2 which includes a hydrogen feed in step (a) of 1,000-40,000 SCF/B of said charge stock. 